It mirrors the content of block devices such as hard disks, partitions, logical volumes etc. It involves a copy of data on two storage devices, such that if one fails, the data on the other can be used. You can think of it somewhat like a network RAID 1 configuration with the disks mirrored across servers. Originally, DRBD was mainly used in high availability HA computer clusters, however, starting with version 9, it can be used to deploy cloud storage solutions.
In this article, we will show how to install DRBD in CentOS and briefly demonstrate how to use it to replicate storage partition on two servers. DRBD is implemented as a Linux kernel module.
In addition, if your system has a firewall enabled firewalldyou need to add the DRBD port in the firewall to allow synchronization of data between the two nodes. Now that we have DRBD installed on the two cluster nodes, we must prepare a roughly identically sized storage area on both nodes. For the purpose of this article, we will create a dummy block device of size 2GB using the dd command. DRBD supports three distinct replication modes thus three degrees of replication synchronicity which are:.
Important : The choice of replication protocol influences two factors of your deployment: protection and latency. And throughputby contrast, is largely independent of the replication protocol selected. A resource is the collective term that refers to all aspects of a particular replicated data set.
Add the following content to the file, on both nodes remember to replace the variables in the content with the actual values for your environment.
Take note of the hostnameswe need to specify the network hostname which can be obtained by running the command uname -n. Also note that if the options have equal values on both hosts, you can specify them directly in the resource section. To interact with DRBDwe will use the following administration tools which communicate with the kernel module in order to configure and administer DRBD resources:.
After adding all the initial resource configurations, we must bring up the resource on both nodes. Next, we should enable the resourcewhich will attach the resource with its backing device, then it sets replication parameters, and connects the resource to its peer:.
At this stage, DRBD is now ready for operation. We now need to tell it which node should be used as the source of the initial device synchronization. Once the synchronization is complete, the status of both disks should be UpToDate. Finally, we need to test if the DRBD device will work well for replicated data storage.
Remember, we used an empty disk volume, therefore we must create a filesystem on the device, and mount it, to test if we can use it for replicated data storage. We can create a filesystem on the device with the following command, on the node where we started the initial full synchronization which has the resource with primary role :. Now copy or create some files in the above mount point and do a long listing using ls command :.
Next, unmount the the device ensure that the mount is not open, change directory after unmounting it to prevent any errors and change the role of the node from primary to secondary :.
On the other node which has the resource with a secondary rolemake it primary, then mount the device on it and perform a long listing of the mount point. If the setup is working fine, all the files stored in the volume should be there:.CentOS 7 Clustering
DRBD is extremely flexible and versatile, which makes it a storage replication solution suitable for adding HA to just about any application. Feel free to share your thoughts with us via the feedback form below.
I know that DRBD needs it's own unmounted dedicated partition before installation to use for data synchronization and metadata thats why I shrinked the root partition on both servers but I am logically lost because we're talking about webservers here with a lot of running services including but not limited to Apache, MySQL, FTP So what should I do starting from this point, how can I move all these services to the new unmounted partitions without affecting the running servers, how can I secure the communications between the two servers with the minimum delay possible and if VPN is the answer how can I achieve it and am I on the right track regarding Pacemaker, Corosync, DRBD and Stonith or there's still something missing I am not aware of and are they the best choice for my existing setup or not, I did my homework and I tried a lot before asking, it's my first experience on such setup and I really need your technical experience and recommendations and maybe a technical path for me to take to achieve my goal.
Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Asked 6 years, 3 months ago. Active 6 years, 1 month ago. Viewed times. Thanks a lot for taking the time to read my question and have a great day :.
Your scenario sounds like you want the replicated partition to be mounted on both sides at the same time, is that correct? To be precise, that's not a problem of DRBD actually, but of the file systems that run on top of it, because they are designed to be in full control of their underlying block devices. It's very hard to answer your question, because you have a whole bunch of questions and not much details.
Install and Configure DRBD Cluster on RHEL7 / CentOS7
So regarding moving data to the new partitions, at least for MySQL this will quite certainly require a down time of the service. For the webserver you might be able to get around the downtime, by copying the files to the new partition, changing the server config, and then deleting the files from the old partition, but even for the webserver it would certainly be more convenient to get a planned down time for it. Are your setups locally redundant or only between the continents?
I have no problem having 24 hours downtime as long as I get this setup up running and I don't screw the existing setup but the real question is, how can I move these services?
Active Oldest Votes. First of all - this is doable. Be aware that you need to install kmod-drbdxen drbd83 I do not recommend using older versions of drbd.
Nils Nils 7, 3 3 gold badges 25 25 silver badges 69 69 bronze badges. You should really switch to protocol A and raise the write-buffer. I also added a link to my recommended sb-setup. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. The Overflow How many jobs can be done at home? Featured on Meta.Without a cluster environment, if a server goes down for any reason that affects entire production.
In order to overcome this issue, we need to configure servers in cluster so that if any one of the node goes down the other available node will take over the production load. Node name: node1. Here in this demonstration we will configure Active backup bonding mode.
The major benefit of DRBD is data high availability across multiple nodes. Note: A cluster quorum required when more than half of the nodes are online. This does not make sense in a two-node cluster. The stickiness prevent the resources from moving after recovery as it usually increases downtime. Execute following command to set stickiness value. Note master-max: how many copies of the resource can be promoted to master status. Defaults to the number of nodes in the cluster. Note As we see on the above test that, we are able to view the previously created database and as well as able to create new database.
The DRBD resource state is also running primary mode on cluster resource running node and secondary mode on other cluster node. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Execute the following command on cluster nodes to create bonding device. Restart the cluster nodes and load the DRBD module.
Edit DRBD configuration file and create mysql resource file and make the following changes. New drbd meta data block successfully created. Execute the following command to change the mode to primary on one of the cluster node which Initializes Device Synchronization. Now stop and disable the DRBD service if started because this service will be managed through cluster.DRBD Distributed Replicated Block Device is a Linux-based software component to mirror or replicate individual storage devices such as hard disks or partitions from one node to the other s over a network connection.
DRBD makes it possible to maintain consistency of data among multiple systems in a network. DRBD supports three distinct replication modes, allowing three degrees of replication synchronicity. Run the following command on both nodes to install the DRBD software and the all necessaries kernel modules. If it is not loaded automatically, you can load the module to the kernel on both nodes, using the follow command:.
Note that modprobe command will take care of loading the kernel module for the time being on your current session. In the above resource file, we created a new resource drbd0 where Initialize the meta data storage on each nodes by executing the following command on both nodes.
Note: if you get any error to make the node primary, use the following command to forcefully make the node as primary:. We hope this tutorial was enough Helpful. If you need more information, or have any questions, just comment below and we will be glad to assist you! If you like this post please share it with your friends on the social networks using the buttons below.
So I was just able to sync two nodes using your guide. I am still trying to understand how DRBD works, but during the process I got stuck into a couple of issues. Overall, really good post. It helped a lot! I followed the steps correctly but after I initiate drbdadm up drbd0 on both nodes it gives me peer-disk:Inconsistent on Secondary node. Is this normal??? Please consider using drbdtop. Yes drbd-overview will be obseleted soon.
Please use drbdadm status will give you the node status. Without that these will just replicate the data. How to enable the slow query log… April 9, How To Configure nginx as reverse proxy… June 26, How to Install Cockpit on Ubuntu It is used to replicate the storage devices from one node to the other node over a network. It can provide assistance to deal with Disaster Recovery and Failovers.
DRBD can be understood as a high availability for hardware and can be viewed as a replacement of network shared storages. Those systems are defined as Primary node and Secondary node can switch Primary and Secndary nodes. First we need to install DRBD packages which is used to create a virtual disk drbd0.
We now work only on drbd0 device. Since drbd0 can only be mounted on Primary node,the contents are only accessed from primary node at a time. By anyway if the primary system crashes out, we may lose the system files, but the virutal device drbd0 will be available.
Read this to learn how to check CentOS version. Here we follow the installation by adding epel repository since drbd packages are not available at centos distributions.
GPG-key is the public key used to encrypt the communication between nodes. Now we can use yum to install drbd packages. We must identify the drbd versions supported by our kernel. You need to reboot the system and try:. To make the modules be loaded during each boot, systemd-modules-load service is used. So, create a file called drbd. The create-md command must be success then after.
After logical device made usable, attach the drbd0 device to sdb1 disk on both nodes. See the output of lsblk. This can be done only on one of the nodes. Here, we format drbd0 as ext3. NOTE: Always remember the process. First, you should make the node as primary for DRBD.No shared storage will be required. At any point in time, the MariaDB service will be active on one cluster node. The convention followed in the article is that [ALL] denotes a command that needs to be run on all cluster nodes.
A simplified network configuration can be seen below. Network configuration for the first node can be seen below, it is the same for the second node except the IPs which are specified above. This article uses Iptables firewall. Authenticate as the hacluster user. DRBD refers to block devices designed as a building block to form high availability clusters.
This is done by mirroring a whole block device via an assigned network. If case we run into problems, we have to ensure that a TCP port is open on a firewall for the DRBD interface and that the resource name matches the file name. For data consistency, tell DRBD which node should be considered to have the correct data can be run on any node as both have garbage at this point :.
If we want to store the data in a different directory, we can use the semanage command to add file context. Please be advised that changes made with the chcon command do not survive a file system relabel, or the execution of the restorecon command.
Always use semanage. At this point our preparation is complete, we can unmount the temporarily mounted filesystem and stop the MariaDB service:. One handy feature pcs has is the ability to queue up several changes into a file and commit those changes atomically. Be advised that a node level fencing configuration depends heavily on environment. Defaults to the number of nodes in the cluster, clone-node-max : how many copies of the resource can be started on a single node, notify : when stopping or starting a copy of the clone, tell all the other copies beforehand and when the action was successful.
Tell the cluster that the clone resource MySQLClone01 must be run on the same node as the filesystem resource, and that the clone resource must be started before the filesystem resource. This is to ensure that all other resources are already started before we can connect to the virtual IP. I have to agree with this one, not that many constructive articles for CentOS 7 on the net.
Install Corosync and Pacemaker On CentOS 6.5
Hi Thomas, Excelent post. Why did you choose to replicate databases by files and not using mysql replication implementation? Do you know if is slower than syncing by the classic method? Sorry for the late reply but my deadline is closing in and im very busy with the documentation.
I managed to get it up and running correctly. The error had something to do with the constraints. I followed your guide on this. Now the cluster worked like i said in the previous comment. Later i decided to give the constraints another try. I had one combining stonith device and filesystem. Now my cluster works with the following constraints. Many thanks for your article. Currently, I am trying to deploy it through a two servers in VirtualBox. I have a question regarding the interfaces.
For each IP address I would like to know which interface do you have to create it through vagrant.Pacemaker is a sophisticated, feature-rich, and widely deployed cluster resource manager for the Linux platform. At its core, Pacemaker is a distributed finite state machine capable of co-ordinating the startup and recovery of inter-related services across a set of machines.
Pacemaker achieves maximum availability for cluster services aka resources by detecting and recovering from node and resource-level failures by making use of the messaging and membership capabilities provided by a preferred cluster infrastructure either OpenAIS or Heartbeat.
Pacemaker is a continuation of the CRM aka v2 resource manager that was originally developed for Heartbeat but has since become its own project. As of RHEL 6.
The pcs package provides a command-line tool for configuring and managing the corosync and pacemaker utilities. The pcs command line interface provides the ability to control and configure corosync and pacemaker. For resilience, every cluster should have at least two Corosync read: heartbeat rings and two fencing devices, to eliminate a single point of failure.
The convention followed in the series is that [ALL] denotes a command that needs to be run on all cluster machines. Network configuration for the first node can be seen below, it is the same for the second node except the IPs which are specified above. This article uses Iptables firewall. If we inspect the raw output, we can see that the Pacemaker configuration XML file contains the following sections:. A cluster has quorum when more than half of the nodes are online.
However, this does not make much sense in a two-node cluster; the cluster will lose quorum if one node fails. Hi, Congratulations for the how-to When I do these: [pcmk01] pcs cluster auth pcmkcr pcmkcr -u hacluster -p passwd. The error message indicates a communication problem.
It might be due to misconfigured firewall is cluster traffic allowed? Thanks do you have reason. I miss configuration in node 2. Other question. These setup is possible in virtual machines nodes? I mean, the VIP should I create in both nodes? How change fron one node to other? Have you configured firewall rules to allow cluster traffic between the nodes?
You can use this setup with virtual machines, in fact, I used VMware when I was configuring cluster nodes part 4 covers VMware fencing. The VIP will be assigned to the active cluster node. Your email address will not be published.
Before We Begin Pacemaker is a sophisticated, feature-rich, and widely deployed cluster resource manager for the Linux platform. We will build a failover cluster, meaning that services may be spread over all cluster nodes. Pacemaker Stack A Pacemaker stack is built on five core components: libQB — core services logging, IPC, etcCorosync — membership, messaging and quorum, Resource agents — a collection of scripts that interact with the underlying services managed by the cluster, Fencing agents — a colllection of scripts that interact with network power switches and SAN devices to isolate cluster members, Pacemaker itself.
Note that the original cluster shell crmsh is no longer available on RHEL.